In the administration of intravenous fluids such as parenteral solutions, physicians frequently desire a connection of two different containers of parenteral solution to the same set, which communicates with a single intravenous needle in communication with the venous system of a patient. For example, the CONTINU-FLO.sup.T.M. intravenous solution set, sold by Travenol Laboratories, Inc. of Deerfield, Illinois, utilizes fluid flow tubing having a connector on one end for connection with a parenteral solution bag or bottle, and a needle adaptor on its other end for intravenous connection with a patient. A Y-site is positioned on the set, capable of connection with an ADD-A-LINE.sup.T.M. intravenous solution set, which is also sold by Travenol Laboratories. This latter set is capable of connection at its other end with a second parenteral solution source.
Accordingly, a set-up of the two above-mentioned parenteral solution sets can be used to administer two different solutions. For example, the CONTINU-FLO set may be connected as a first set to a container of normal saline or dextrose solution. The ADD-A-LINE set may be connected, as a second set in connection with the first set, to a container of antibiotic solution. Hence, a slow, continuous drip of normal saline or dextrose may be administered to the patient, for maintenance of an effective parenteral liquid connection with the patient's venous system. This permits the immediate, intermittent administration of the antibiotic as needed over a period of time.
While a continuous drip of normal saline or dextrose solution is required for preventing blood clotting in the needle, it is generally desired for the overall amount of such solution administered on a continuous basis to be very small. In fact, frequently, the desired flow rate can be so low that the conventional drip chamber of an administration set forms drops (about 10 drops per c.c. of fluid administered) which are large enough to fall so infrequently from the drop former of the drip chamber that it becomes difficult and time-consuming to accurately measure the drip rate. Accordingly, the overall fluid administration rate of the set is not easily monitored.
In response to this, parenteral administration sets are sold in which a small drop forming tube is utilized in the drip chamber. This tube may have an inner diameter of typically about 0.02 to 0.03 inch. Such a constricted drop forming chamber in a drip chamber is capable of producing smaller drops, for example, about 60 drops per c.c. of liquid administered. Accordingly, at the same low flow rate, drops of liquid will fall through this drip chamber at a rate six times faster than they would through a large drop forming a drip chamber of ten drops per c.c.
While the above small-drop arrangement is a satisfactory solution for the determination of flow through an administration set at low flow rates, a problem is created in the situation where a pair of solution sources are connected together for intermittent, alternate fluid administration to a patient through a single needle. The problem is that, when a small drop forming member is used in a drip chamber, and a higher overall fluid flow is desired, a suction pressure head can develop in the tubing downstream from the drip chamber. This is so because the small drop forming member may provide an inadequate fluid flow to resupply the set, as solution is administered at a high rate to a patient, impelled by the gravity pressure of the fluid column in the administration set (or alternatively by a pump).
As a result of this, in gravity-operated sets, if the connection site of the second set with the first set is positioned remotely from the patient and near the drip chamber mentioned above, and if the parenteral solution source connected to the second set becomes empty, air may be sucked into the parenteral solution set through the second set. The same event can also take place in pumped sets.
Thereafter, the administration of a second aliquot of solution from the first source of parenteral solution may actually cause air to be forced into the patient, which is extremely undesirable and dangerous. Alternatively, if the presence of air is noticed, the sets may have to be disconnected and reprimed to eliminate air.
The above problem exists whenever an air access site exists in the set, particularly in its upper portion in position of use, where a substantial suction pressure head can form to cause air to be drawn into the set.
While this problem can, in gravity operated sets, be reduced in scope when the access site is positioned lower and nearer to the patient, this can be undesirable, since it brings the site within reach of the patient, and thus is more subject to being tampered with and the like. Furthermore, a downstream connection of primary and secondary sets produces more of a tangle of tubing at the patient's bedside.
The invention of this application overcomes the above difficulties, in that it provides, for the first time, a means whereby an administration set may be safely used with a patient, even though (1) a constricted drop-forming member is used, and (2) an air-access site to the set is vertically elevated, near the drip chamber and the hanging sources of parenteral solution, and away from the patient.
Accordingly, by this invention, the advantages of a constricted drop-forming member of the drip chamber can be achieved, without running the risk of infusing air into the patient. This has hitherto been inherent in the use of such a small-drop drip chamber in conjunction with a connected pair of sets and separate sources of parenteral solution.